Innate Immunity Overview

Innate Immunity

• Innate immunity is a natural, inborn barrier against microorganisms.
• Its primary function is to prevent or limit infections by bacteria, viruses, fungi, and parasites.
• This defense is performed by various cellular and humoral components interacting to coordinate an immune response that eliminates pathogens or minimizes damage.
• Innate immunity acts as a first line of defense against infectious agents, checking them before they cause significant infection.

Objectives

• Defining immunity and the immune system's two main components.
• Identifying the first defense line of innate immunity.
• Identifying the second defense line of innate immunity.
• Understanding phagocytosis and its stages.
• Defining opsonization.

Types of Immunity

• The immune system consists of innate and adaptive immunity, working together.
• Innate immunity, the first line of defense, is non-specific.
• Adaptive immunity is called upon if innate defenses fail; it targets specific pathogens.

Components of Innate Immunity

• First Line of Natural Defense:
  • Mechanical barriers (intact skin, mucous membranes, hair in nares, coughing, sneezing, and blinking reflex/tears).
  • Chemical barriers (sweat, sebaceous secretions, lysozyme, acidic pH).
  • The normal microbiota (which suppress the growth of pathogenic bacteria and fungi).
• Second Line of Natural Defense
  • Circulating effector proteins (lysosome, complement, acute phase proteins, interferons).
  • Cells of innate immunity (phagocytes, natural killer (NK) cells)
  • Inflammatory barriers

Cells of the Immune System

• The immune system's cells originate from stem cells.
• The stem cells differentiate into lymphoid stem cells and myeloid progenitor cells, resulting in diverse cell types (B cells, T cells, natural killer cells, neutrophils, macrophages dendritic cells etc.).

Phagocytosis

• Phagocytes (i.e., macrophages and neutrophils) are specialized for capturing, engulfing, and destroying invading microorganisms.
• The process of phagocytosis involves chemotaxis and migration, attachment, ingestion, and intracellular killing or digestion.
• Killing or digestion occurs via oxygen dependent pathways (radical oxygen production) or oxygen independent pathways using enzymes.

Opsonization

• Enhanced Attachment and ingestion of organisms, coating microbes with opsonins (antibodies and complement).
• Opsonization is the process of coating an organism to enhance phagocytosis.
• It's aided by activated complement C3b or antibodies.

Natural Killer (NK) Cells

• Large granular lymphocytes with non-specific cytotoxic activity against tumor cells, virus-infected cells, and graft cells.
• They are essential to innate immunity.

Inflammatory Barriers

• Includes vasodilation, increased capillary permeability, and fluid/cell influx into tissues.
• Characterized by redness, increased temperature, swelling (edema), and influx of phagocytes into tissues.
• Initiated by chemical mediators (released from damaged tissues or microbes, by plasma-enzyme systems, or by leucocytes).

Cytokines in Innate Immunity

• Cytokines like IL-1, IL-6, IL-8, and TNF-α are crucial pro-inflammatory cytokines in innate immunity.

Constitutional Factors Affecting Immunity

• Differences in species susceptibility to pathogens
• Racial variations in susceptibility.
• Genetic variations in individuals within the same race.
• Age differences impacting immune system development and function (immaturity in children versus aging).
• Nutritional status affects immunity (under-nutrition reduces immunity).
• Hormonal influences and corticosteroids decrease immune response.
• Specific examples include diabetics being more susceptible to infections.

Explore the essential concepts of innate immunity, the body's first line of defense against pathogens. This quiz covers the definition, key components, and functions of innate immunity, including phagocytosis and opsonization. Test your knowledge on how innate immunity interacts with adaptive immunity to protect against infections.